This invention relates to a method for grinding a contoured surface on a workpiece, and more particularly, to a method for automatically assuring that the surface is automatically ground to a particular size.
Conventional grinding of contoured surfaces in a workpiece can be accomplished by use of a grinding tool mounted on a jig grinder. The tool, of cylindrical configuration, is mounted on a high speed rotatable grinding spindle. The machine also has a spindle which moves relative to an X and Y axis as well as vertically along a Z-axis, and can rotate about its own centerline and is known as the C-axis or machine spindle centerline. The tool is independently movable relative to the machine spindle and machine spindle centerline of the jig grinder along what is commonly termed as the U-axis, and can also rotate about its own centerline or spindle shaft.
The relative movement of the machine spindle of the jig grinder and tool along any combination of these axes can be automatically controlled by a computerized program to grind the workpiece in a contoured predetermined pattern which will result in a contoured shape. Alternatively, the grinding process can be performed manually.
This invention relates to a method for assuring that the ground shape of the contoured surface is properly dimensioned or automatically sized.
In accordance with the invention, a detector having a reference edge position is provided adjacent the rotatable machine spindle of the jig grinder. The machine spindle centerline of the jig grinder is moved a distance from the detector's reference edge equal to the finished radius size of the surface to be ground or any known distance, to be used as a datum. Using the U-axis, the tool or grinding wheel which is above the detector's edge, is moved relative to the jig grinder centerline to clear the detector's pick-up edge. Then, with the grind side of the grinding wheel facing the detector pick-up edge, and the grinding wheel in a grinding mode, the wheel is lowered and outfed back along the U-axis until the outermost cutting position of the grind side of the grinding wheel position is equal to or in some repeatable proximity to the position of the reference edge, as for example where the wheel just barely scrapes or makes contact with the detector pick-up edge, which can be confirmed by laser, force or sound apparatus. When this condition is present, the outfeed is instantly stopped with no over-travel. This U-axis radial position relative to the position of the C-axis spindle or static centerline of the jig grinder is automatically sized radius value to be ground in the workpiece and is the preset size or datum radial position to which the tool is to be moved during the grinding mode.
The jig grinder C-axis centerline can then be positioned by movement along a combination of the X and Y axes to the centerline (in plan evaluation) of, e.g., a hole to be ground in a workpiece, or an arcuate contoured surface which is to be ground. The tool with its spindle is then positioned to clear stock on the workpiece by movement along the U-axis relative to the jig grinder C-axis centerline (and raised and lowered along the Z-axis as necessary to clear the workpiece) and entered into the hole to be ground. With the grinding surface of the tool in contact with the stock, the tool is outfed along the U-axis back to the preset radius position or any other radius using the preset as a datum while using whatever conventional grinding methods and techniques are specified. When grinding is complete (i.e., all material has been ground away), and the grinding wheel is in its relative preset position, the surface has been automatically sized.